The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Engine control systems manage air and fuel delivery to the engine based on either open loop or closed loop feedback control methods. Open loop control methods are typically initiated during specific operating conditions such as start up, cold engine operation, heavy load conditions, wide open throttle, and intrusive diagnostic events, etc. An engine control system typically employs closed loop control methods to maintain the air/fuel mixture at or close to an ideal stoichiometric air/fuel ratio. Closed loop fuel control commands a desired fuel delivery based on an oxygen content in the exhaust. The oxygen content in the exhaust is determined by oxygen sensors that are located downstream of the engine.
Oxygen sensors generate a voltage signal proportional to the amount of oxygen in the exhaust. Oxygen sensors typically compare the oxygen content in the exhaust with an oxygen content in the outside air. As the amount of unburned oxygen in the exhaust increases, the voltage output of the sensor drops. Most oxygen sensors must be heated before they can effectively operate. Heater elements present in the oxygen sensor heat the sensor to a desired operating temperature.
Cracking of oxygen sensor elements may occur due to thermal shock. Cracking is thought to be due to water droplets, which are produced by combustion and borne by the exhaust gas stream, coming in contact with a ceramic element of the oxygen sensor. While the engine warms up, moisture can be present in the exhaust system. In some cases, the liquid moisture, entrained by the passing gas flow, may come in to direct contact with the oxygen sensor elements. If the element has, by this point in time, reached a hot enough temperature, the water droplet can cause the ceramic element to crack.